The atom chip is a device aimed at realizing quantum technology devices in which the rules of quantum mechanics are used to realize applications such as ultra sensitive clocks, gravitation and acceleration sensors, quantum cryptography (secure communications), and quantum computing, to name a few.
A typical, conventional atom chip is composed of a substrate upon which an electrically conductive functional layer is disposed. In the case that the substrate is not electrically insulating, a layer of electrically insulating material will be disposed between the substrate and the functional layer. The Atom Chip's conducting element, through which an electrical current flows creating a magnetic field in case of DC electrical current or electromagnetic field in case of AC electrical current, that will be referred to as internal fields, is within the functional layer, as a part of it, beneath it, or in any other suitable structure. The form of the Atom Chip's conducting element determines the distribution of potentials of the internal fields, which affect the trapping performance. This form can be Z-shaped, U-shaped, in a conveyer belt shape or in a variety of other shapes or combinations of shapes. External bias fields are necessary in many cases.
The atom chip device is located within an ultra high vacuum chamber. Commonly, the atom trapping on atom chips is by means of only magnetic fields. In the more advanced atom chip devices, atoms within the vacuum chamber are influenced by internal magnetic and electric fields, by light fields whose sources can be laser sources, some of which are reflected by the functional layer, if it has a minor nature, and by electrical fields and magnetic fields generated by elements outside of the vacuum chamber, which will be referred to as external fields. The combination of these influences, if performed correctly, traps cold neutral atoms in very close proximity to the atom chip in the atom micro-trap.
The elements of the atom chip and in particular the functional layer and the atom chip's conducting element are substantially composed of pure metals. Due to harmful effects such as magnetic thermal noises, as well as background noises, the time interval of the atom trapping is limited, the atoms escape the trap, and the cloud that they create fades with time. Additionally, the atoms' temperature can increase with time (heating), and also the coherence of their quantum state may be destroyed (decoherence). The intensity of the magnetic noise increases with reduction of the distance between the trap center and the atom chip surface [5, 6].
The typical lifetime of atoms trapped at the distance of 3 μm from an atom chip surface in a conventional atom chip device is about 0.5 seconds, the magnetic noise portion in the lifetime limitation being 80%, see for example [1]. Typical heating rates for cold atoms several μm from the surface are 300-500 nK/s [2]. For isotropic materials the decoherence rates are approximately as those for trap loss rates due to spin flips (i.e. in the above example 2 s−1) [2]. Reduction of the magnetic noise is needed for all applications of the atom chip. For example, it is important for a quantum gravity gradiometer, where the atom chip is used as an interferometer based gravity sensor. The sensitivity of this device is limited by the magnetic noise [7]. For an atomic clock the magnetic noise limits the frequency stability, which determines the atomic clock precision [8].
Apart from magnetic noise, imperfections in the current-carrying elements on the atom chip lead to time-independent corrugation of the magnetic trapping potential, affecting the density profile of the atom cloud, up to a point where the cloud can break-up into smaller clouds (fragmentation). Fragmentation is directly related to current flow in the current-carrying structures [30], and becomes worse as the atom-surface distance becomes smaller. This corrugation limits on the ability to create extremely tight and smooth trapping potentials.
PCT patent application PCT/IL2006/000118, filed 29.01.2006, which is incorporated by reference for all purposes as if fully set forth herein, describes an atom chip device, whose magnetic noise level is significantly less than that which could be achieved previously in atom chip devices.
There is thus a widely recognized need for, and it would be highly advantageous to have an atom chip device, whose magnetic noise level would be significantly less than that which can currently be achieved in existent atom chip devices.